Guar is derived from the endosperm of the leguminous plant Cyamopsis tetragonolobus (Linue) Taub or Cyamopsis Psoraloides (Lami) D. C. (Fam. Leguminosae).
It is a high molecular weight non-ionic hydrocolloidal polysaccharide, a galactomannan composed of galactose and mannose units. Guar seeds comprise a seed coat or hull, a pair of tough endosperm sections, referred to as `guar splits`, which contain the gum and the embryo. In processing, the hull is removed and the components separated by grinding, sifting and screening in one or more stages. The splits are ground and processed to provide a gum or gum precursor.
The splits may be processed to recover components thereof which may include all membrane, inorganic salts, and the predominant galactomannan, polysaccharide as well as associated proteinaceous material and water insoluble gels. The extraction has typically been achieved by way of hydration and/or alkaline digestion or refining processes as represented by U.S. Pat. No. 4,269,975 to National Starch and Chemical Corporation and U.S. Pat. No. 4,659,811 to Henkel. In the former, a hydration/extrusion operation is said to provide a high viscosity, e.g. 5000 cps finely divided, moisturized guar gum which could be dried and ground for future use. The '811 patent (and cited references such as U.K. Patent No. 906,327) recites the use of an alkaline medium at elevated temperature to separate endosperm from embryo and residual husk. The patentee still employs upwards of 60 percent of water in the reaction mixture, and utilizes a pH above 12, with a minimum of 150 parts by weight of aqueous alkali. The resulting wet solids may be partially neutralized to a pH below about 11, e.g., pH 9 (Example 9).
Other industrial processes have refined natural guar splits with acid solutions, heating the mixture, and then neutralizing the acid with sodium hydroxide or another alkaline material. The resultant product is a functionally modified guar controlled primarily by the pH and time of heat processing. Neutralization by alkaline treatment has tended to result in a high ash content, variability and other characteristics inconsistent with food ingredient use. In these processes effects tend to be concentrated on the exterior portion of the endosperm leading to an irregular non-uniform product with differential levels of functional modification. The property of stringiness manifests itself in processed and dried guar gum products and presents difficulties in food applications where smoothness, slipperiness or greasiness are important qualities to achieve or retain. While modification with chemical processing may minimize this problem it is attended with the ready development of ash, rapidly approaching levels of 1.5% or more, unacceptable for food use.
It is accordingly desirable to provide a process for the refinement of natural guar products to afford a uniform, homogeneous particulate product capable of forming aqueous solutions, pastes and gums of consistent, stable and reliable low viscosity and ash contents below 1.5%, generally below 1.0% for use in food product compositions of enhanced aesthetic character including desirable thickening and smoothening properties with enhanced mouthfeel in addition to other favorable organoleptic properties.